A print head of this type is known from German Pat. No. 2,543,451. Its ink ducts empty by their jet openings on the point of the print head in a grid-like distribution, by which it becomes possible, with a suitable selective triggering the piezoelectric drive element with electrical voltage pulses during a line-by-line movement of the print head, to record characters on a recording support. For this the piezoelectric drive elements in the form of little tubes, as a result of their being triggered with the voltage pulses, cause a corresponding pulse-like contraction of the ink ducts, by means of which pressure pulses are exerted on the ink present in the ink ducts, which in turn leads to the detaching of ink droplets at the jet openings of the ink ducts as well as to their being transferred to the recording support.
One disadvantage of the print heads of this type previously known is that the distance between the jet openings and the recording support cannot be increased at will and for the purpose of generating the most accurate possible mosaic characters can be only 0.5 to 1 mm at most. However there are application cases in which a greater distance from the recording support is required. An example of such an application case is the marking of bank deposit books in banking practice within the scope of an automatic accounting process. For this the page to be marked, depending on its position in the deposit book or on the number of marking operations already done, may be at a long distance or short distance from its print head or its jet opening. Within a distance range which may be 3 mm or more, however, an always constant printing accuracy must be ensured.
If the ink droplets are to be moved with constant accuracy over a long distance to the recording support after emerging from the jet openings, then the pressure pulses causing this must be generated with a higher intensity in order to ensure a droplet flow in a straight line. For this the amplitude of the control voltage pulses applied to the piezoelectric drive elements can be increased, but relatively low limits are imposed on such an increase, which are probably due to the mechanical behavior of the drive element itself and do not lead to the desired result but rather have the effect of greater printing inaccuracies.